The use of blowout preventers in drilling, completion, workover, and production of oil and gas wells is well known. Such blowout preventers generally include a housing with a bore extending through the housing. Opposed chambers extend laterally of the bore in the housing and communicate with the bore. Rams are positioned in the chambers and the rams are connected to rods that are supported for moving the rams inwardly into the bore to close off the bore. This action divides the bore into a zone above the rams and a zone below the rams. The rods also serve to retract outwardly from the bore to open the bore.
Various types of rams may be employed such as those which engage circumferentially around a pipe or tubular member for sealing engagement with the tube or pipe, while others are provided with cutting surfaces for shearing tubular members or cables which extend through the bore of the blowout preventer.
Blowout preventers are also commonly used in coiled tubing systems. Such a BOP provides a means of holding the tubing and isolating the well bore pressure during a variety of conditions, including emergencies. The configuration of the BOP rams and sideport facility allows well-control operations to be conducted under a variety of conditions.
Newer blowout preventers include four sets of rams, which may be referred to herein as a "Quad BOP". The system comprises a set of four stacked elements, each with a different function. Blind rams are shut when there is no tubing or tool string extending through the body of the BOP. Shear rams are designed to close on and cut through the tubing. Slip rams close on and hold the tubing, ideally without damaging the surface of the piping or other tubular member. Finally, pipe rams seal around the tubing when it is place. Each of the rams should only be actuated when the tubing is stationary; otherwise, damage to either the BOP or the tubing is likely.
Stacking the four BOP elements one on top of the other has been found to unnecessarily extend the height of the Quad BOP. Further, the four elements are massive and consequently add a great deal of weight to the well head. In order to reduce the height and weight of the stack, certain Quad BOPs combine the primary actuators for each of the slip and the pipe ram. This has accomplished the intended purpose of reducing the height and weight of the stack but, unfortunately, eliminates the independent actuation of these elements.
Although slip rams ideally do not damage the tubing surface of the tubular member through the BOP, it has been found that even a single actuation of the slips against the tubing can score the exterior surface of the tubing. In today's high performance operations at elevated pressures, this scoring can reduce the useful lifetime of the tubular member, particularly with coiled tubing. Thus, there remains a need for the capability to actuate the pipe rams without actuating the slip rams, with the actuation elements included within a single ram body.
There remains a further need for a blowout preventer that is reduced in height and weight but which retains independently actuatable BOP rams. Such a blowout preventer should include the operations of two such ram elements, retaining their independent actuation, within a single ram body or chamber.